1. Field of the Invention
This invention relates to a microlens array comprising a plurality of microlenses disposed regularly in a linear or planar arrangement and it also relates to a method for producing the same.
The microlens array of this invention can be used in the following applications i-iii.
(i) A means for condensing illuminating light on the picture element regions of a nonluminescent display device such as a liquid crystal display device to increase the brightness of the display (see, e.g., Japanese Laid-Open Patent Publications No. 60-165621, No. 60-165622, No. 60-165623, No. 60-165624, and No. 60-262131). PA1 (ii) A means for condensing incident light or a means for forming an image, on the photoelectric conversion regions of a solid-state image sensing device such as a charge coupled device (CCD) or of a line image sensor used in facsimiles and the like to improve the sensitivity of these devices (see, Japanese Laid-Open Patent Publications No. 54-17620 and No. 57-9280). PA1 (iii) A means for forming an image to be printed, on a photosensitive means used in liquid crystal printers or light emitting diode (LED) printers (see, e. g. , Japanese Laid-Open Patent Publication No. 63-44624). PA1 (1) A method for forming a plastic or glass material by the use of a mold. PA1 (2) A method for forming convex lenses on the basis of a phenomenon in which when a photosensitive resin is exposed to light in a desired pattern by the use of an aligner, unreacted monomers move from the unexposed regions to the exposed regions, resulting in a swell of the exposed regions (see, e.g., Journal of the Research Group in Microoptics Japanese Society of Applied Physics, Colloquium in Optics, Vol. 5, No. 2, pp. 118-123 (1987) and Vol. 6, No. 2, pp. 87-92 (1988)). PA1 (3) A method for obtaining convex lenses wherein a pattern of the lenses in a planar configuration is drawn on a thermoplastic resin by a conventional photolithographic technique or the like, and then the thermoplastic resin is heated to a temperature above the softening point of this resin to have flowability, thereby causing a sag in the pattern edge (see, e.g., Japanese Laid-Open Patent Publications No. 60-38989, No. 60-165623, and No. 61-67003). In this method, when the thermoplastic resin used has a photosensitivity, a pattern of the lenses can be obtained by exposure of this resin to light. PA1 (4) A method for obtaining convex lenses wherein a photosensitive resin is exposed to light by a proximity exposure technique in which a photomask is not brought into contact with the resin, to cause a blur at the pattern edge, so that the amount of photochemical reaction products is distributed depending upon the degree of blurring at the pattern edge (see, e.g., Japanese Laid-Open Patent Publication No. 61-153602). PA1 (5) A method for generating a lens effect wherein a photosensitive resin is exposed to light with a particular intensity distribution to form a distribution pattern of refractive index depending upon the light intensity (see, e.g., Japanese Laid-Open Patent Publications No. 60-72927 and No. 60-166946). PA1 (6) A method for obtaining distributed index lenses by a selective ion diffusion, wherein a glass plate which serves as a substrate is immersed in a molten salt to cause an exchange of a different kind of alkali ions or the like between the glass plate and the molten salt through a mask disposed on the glass plate, thereby yielding a glass plate with a distribution of refractive index corresponding to the mask pattern (see, e.g. , Electronics Letters, Vol. 17, No. 18, p. 452 (1981)). PA1 (7) A method for obtaining convex lenses by the use of a contraction accompanying the crystallization of a photosensitive glass caused by illuminating the glass (see, e.g., Applied Optics, Vol. 24, No. 16, p. 2520 (1985)). This method is based on the following principle: When a glass plate which has been coated with a silver salt to have a photosensitivity is exposed to light, silver atoms are liberated to form a latent image made of crystal nuclei. This glass plate is then heated to crystallize around the crystal nuclei, thereby causing a decrease in its volume. When the glass plate is exposed to light with an intensity distribution of a particular pattern, the exposed portions of the glass plate contract, but the unexposed portions do not contract and therefore are left to form relatively protuberant portions, resulting in a configuration of convex lenses through surface tension.
2. Description of the Prior Art
A conventional microlens array can be formed by any one of the following methods 1-7.
FIG. 4a shows a conventional microlens array 40 produced by this method. The microlens array 40 consists of a supporting substrate 41 and a light condensing layer 42 having a plurality of microlenses, disposed thereon. This microlens array is produced as follows.
First, as shown in FIG. 4b, the supporting substrate 41 is provided to support the light condensing layer 42 having the microlenses. Then on the upper surface of the supporting substrate 41, a photosensitive resin layer 43 is formed as shown in FIG. 4c. Thereafter, with the use of a separate shading mask 44, the upper surface of the photosensitive resin layer 43 is illuminated with light from a mercury lamp or the like, so that the photosensitive resin layer 43 is exposed to the light. As a result, the exposed portions of the photosensitive resin layer 43 swell into the shape of convex lenses as shown in FIG. 4d, to form the light condensing layer 42 having a plurality of microlens. In this way, the conventional microlens array 40 is obtained which is shown in FIG. 4a.
In a microlens array made by any one of the above-mentioned methods 1-7, a separate shading mask must be provided to prevent the adverse effects of stray light (undesirable light) on the display characteristics, such as a decrease in contrast. However, this arrangement introduces another problem of having a deviation between the position of the microlens array and the corresponding position of the shading mask, which causes a decrease in the availability of incident light, resulting in degradation of the display characteristics.
Moreover, method 1 above is limited due to the inability of machines to process a mold with high density and high dimensional accuracy. Also methods 6 and 7 cannot provide a high reliability in the dimensional accuracy for practical applications, because glass materials are treated at high temperatures.